Research

4D Electron Microscopy

​We have established and developed the second generation of four-dimensional (4D) scanning ultrafast electron microscopy (S-UEM) and demonstrate the ability to record time-resolved images (snapshots) of material surfaces with 650 fs and ~ 5 nm temporal and spatial resolutions, respectively.
Using S-UEM, we spatially and temporally visualize the charge carrier dynamics on the surface of InGaN NW arrays before and after surface passivation with octadecylthiol (ODT).
​Here, we precisely map the surface charge carrier dynamics of the CIGS before and after surface passivation in space and time.
​By visualizing different surface of CdSe single crystals, we show that the morphology, grains and nanostructure features of the material surface can impact the overall carrier relaxation processes.
​Using our S-UEM with a 650 fs and ~5 nm temporal and spatial resolutions, respectively, we show that time resolved imaging of the energy loss dynamics and carrier spreading on the surfaces of a densely packed array of InGaN nanowires (NWs) as a model system can be achieved now in real space.

Ultrafast Laser Spectroscopy

​We studied the quantum confinement-tunable ultrafast charge transfer at the PbS quantum dot and phenyl-C61-butyric acid methyl ester (PCBM) interface as a model system.  In this work, we added a piece to the puzzle with a careful investigation into how light affects electrons at the space between PbS QDs and PCBM electron accepting components commonly used in solar cells.
​We carefully selected three porphyrin structures with different charge localizations of the meso unit and different redox properties of the porphyrin cavity to understand the ultrafast electron injection event at the GC–porphyrin interface from the molecular structure point of view.
​We applies several laser spectroscopic techniques using a variety of QDs including Ag2S QDs, PbS QDs, and CdTe QDs not only to assess multi-carrier generation and intra-band relaxation pathways in semiconductor QDs, but also to understand the electronic states, including hot electrons involved in the excited QDs.
​We developed a layer-by-layer (LbL) protocol as a facile, room-temperature, solution-processed method to prepare electron transport layers with a controlled and tunable porous structure, which provides large interfacial contacts with the active layer.
​We have an especial interest in the effect of the incorporation of heavy metals into p-conjugated chromophores for the exploration of the triplet state and its impact on solar cells, and as such are exploring metallated DPP derivatives.
We extended our research activities using the state-of-the-art laser spectroscopy to newly synthesized silver nanoclusters.
​We explored perovskite oxide SrTiO3 (STO) for the first time as the electron-transporting layer in organolead trihalide perovskite solar cells to contribute on the breakthrough of perovskite-based solar cells power conversion efficiency.